1. Field of the Invention
The present invention relates to inductor structures, and, more particularly, to a symmetric differential inductor structure.
2. Description of Related Art
In the field of semiconductor fabrication processes, differential inductors are important passive components. Generally, there are two types of differential inductors: symmetric differential inductors and center-tap differential inductors.
FIG. 1A shows a symmetric differential inductor 1. Referring to FIG. 1A, the symmetric differential inductor 1 has a T-shaped central conductive wiring 10 disposed in the center of a substrate, a first conductive wiring 11 extending from the left side of the central conductive wiring 10 in a counterclockwise spiral (moving outwards from the center), and a second conductive wiring 12 extending from the right side of the central conductive wiring 10 in a clockwise spiral. One end of the first conductive wiring 11 has a first input port 110 and the other end of the first conductive wiring 11 has a contact 111 connected to the left side of the central conductive wiring 10. One end of the second conductive wiring 12 has a second input port 120 and the other end of the second conductive wiring 12 has a contact 121 connected to the right side of the central conductive wiring 10. FIG. 1B shows characteristic curves and quality factors of the symmetric differential inductor 1.
FIG. 2A shows a center-tap differential inductor 2. Referring to FIG. 2A, the center-tap differential inductor 2 has a central conductive wiring 20, a first spiral conductive wiring 21 and a second spiral conductive wiring 22. One end of the first spiral conductive wiring 21 has a first input port 210 and the other end of the first spiral conductive wiring 21 has a contact 211 connected with the central conductive wiring 20. One end of the second spiral conductive wiring 22 has a second input port 220 and the other end of the second conductive wiring 22 has a contact 221 connected to the central conductive wiring 20. The first spiral conductive wiring 21 has a third conductive wiring section 23 extending across the second spiral conductive wiring 22, and the second spiral conductive wiring 22 has a fourth conductive wiring section 24 extending across the first spiral conductive wiring 22. FIG. 2B shows characteristic curves and quality factors of the center-tap differential inductor 2.
However, the T-shaped central conductive wiring 10 of the symmetric differential inductor 1 and the central conductive wiring 20 of the center-tap differential inductor 2 occupy a large area of the substrate, thereby decreasing the product profit. Further, it is not possible to attain a fully symmetric structure due to the intersections of the spiral conductive wirings in the center-tap differential inductor 2. As such, phase differences or other interference could occur and adversely affect the product yield and even seriously affect the inductance values and quality factors of the inductor.
Therefore, it is imperative to provide a differential inductor structure different from the conventional symmetric or center-tap differential inductors so as to overcome the above-described drawbacks.